This invention relates generally to medical devices and more particularly to systems for monitoring intracranial pressure of a living being.
Numerous patents have been issued disclosing various means for monitoring intracranial pressure by means of an implant to sense such pressure and provide a signal representative thereof to some externally located means. The following constitutes United States Patents relating to such technology:
U.S. Pat. No. 3,853,117 (Murr) discloses a pressure-sensing system and method which makes use of ultrasound to interrogate a deformable, implantable device.
U.S. Pat. No. 3,943,915 (Severson) discloses an intracranial pressure monitoring device which incorporates a lumped-constant tuned circuit, with a capacitor whose plate separation varies as a function of pressure.
U.S. Pat. No. 3,977,391 (Fleischmann) discloses a pressure sensor apparatus which uses a radionuclide source in an arrangement with shielding that provides for variable ionizing radiation output with applied pressure. The device includes a mechanical or hydraulic motion amplification system, with associated moving parts.
U.S. Pat. No. 4,003,141 (LeRoy) discloses several intracranial pressure sensors, including an implantable one that is based on the external detection of a change in a magnetic field when an implanted sensor incorporating a magnet is deformed.
U.S. Pat. No. 4,014,319 (Favre) discloses an intracranial pressure transducer using an implanted magnet to vibrate in an externally applied magnetic field, the frequency of vibration varying according to the pressure.
U.S. Pat. No. 4,026,276 (Chubbuck) discloses an intracranial pressure monitor in the form of an implantable intracranial sensor using a metal bellows containing a gas as the deforming element. This element is linked to one plate of a capacitor in a lumped-constant tuned circuit.
U.S. Pat. No. 4,062,354 (Taylor et al.) discloses an intracranial pressure transducer system using an implanted active circuit including a power receiver and tunnel-diode oscillator.
U.S. Pat. No. 4,114,606 (Seylar) discloses a monitoring apparatus for resonant circuit intracranial pressure implants. The apparatus includes a resonance-detection device for use with implantable resonant circuits, like those described in U.S. Pat. No. 4,026,276. An external monitoring circuitry in the form of an RF sweep generator is provided to monitor its own output.
U.S. Pat. No. 4,127,110 (Bullara) discloses an implantable pressure transducer incorporating a sliding bearing and a fluid-filled link to the intracranial space.
U.S. Pat. No. 4,186,749 (Fryer) discloses an induction powered biological radiosonde in the form of a variable capacitor pressure transducer as part of a tuned circuit. The tuned circuit varies the frequency of an induction-powered oscillator.
U.S. Pat. No. 4,206,761 (Cosman) discloses a pressure-balanced telemetric pressure sensing method.
U.S. Pat. No. 4,206,762 (Cosman) discloses a telemetric differential pressure sensing method using a flexible polymer membrane and a sliding bearing. Most of the embodiments described require that the scalp transmit atmospheric pressure faithfully to the device.
U.S. Pat. No. 4,246,908 (Inagaki et al.) discloses an intracranial pressure transducer based on a piezo-electric or semiconductive pressure sensor. This device is not a permanently implantable, nor a remote device.
U.S. Pat. No. 4,265,252 (Chubbuck et al.) discloses an intracranial pressure implant using a bellow and a capacitive pressure sensor.
U.S. Pat. No. 4,281,667 (Cosman) discloses a single diaphragm telemetric differential pressure sensing system which appears to be an improvement of the system of U.S. Pat. Nos. 4,206,761 and 4,206,762.
U.S. Pat. No. 4,354,506 (Sakaguchi et al.) discloses an intracranial pressure gauge. This patent describes both variable capacitor and variable inductor methods of detecting the deflection of a diaphragm using a lumped-constant tuned circuit.
U.S. Pat. No. 4,378,809 (Cosman) discloses audio-telemetric pressure sensing systems and acoustic methods of interrogating the sensors like those of U.S. Pat. Nos. 4,281,667, 4,206,761 and 4,206,762.
U.S. Pat. No. 4,471,786 (Inagaki et al.) discloses a telemetering intracranial pressure transducer which requires an internal battery for power, a pressure-transmitting flexible plastic membrane and a complex active circuit.
U.S. Pat. No. 4,494,411 (Koschke et al.) discloses a pressure detector comprising a cylindrical cavity resonator having a front surface made as a diaphragm and using a coaxial cavity with a helical winding and ceramic core. The device requires an active circuit within it and a highly elastic, conductive metal diaphragm.
U.S. Pat. No. 4,593,703 (Cosman) discloses a telemetric differential pressure sensor with the improvement of a conductive shorted loop tuning element and a resonant circuit, e.g., an implantable tuned circuit having a deflectable diaphragm with the inductive element coupled to the diaphragm.
U.S. Pat. No. 4,653,508 (Cosman) discloses a pressure-balanced telemetric pressure sensing system and method. The system requires the placing of a pressure transducer against a detection chamber which has been implanted just under the scalp. The detection chamber is connected via a fluid path to the intracranial space.
U.S. Pat. No. 4,660,568 (Cosman) discloses a telemetric differential pressure sensing system and method making use of an implanted flexible plastic membrane, a fluid channel, and a sliding bearing. In some embodiments, capacitive or inductive coupling through the scalp is used.
U.S. Pat. No. 4,676,255 (Cosman) discloses a telemetric in-vivo calibration method and apparatus using a negative pressure applicator. This patent discloses a way to calibrate an implanted sensor of the type described in U.S. Pat. Nos. 4,660,568, 4,378,809, 4,281,667, 4,206,761 and 4,206,762.
U.S. Pat. No. 4,738,267 (Lazorthes et al.) discloses an implantable, intracranial-pressure sensor, in the form of a resistive strain gauge which is not self-contained.
U.S. Pat. No. 4,926,696 (Haritonidis et al.) discloses an optical micropressure transducer which requires a clear optical path to and from the sensing element.
U.S. Pat. No. 5,018,529 (Tenerz et al.) discloses a miniaturized sensor for physiological pressure measurements which utilizes external illumination delivered by an optical fiber and returns its signal through that fiber.
U.S. Pat. No. 5,317,917 (Dufour) discloses a resonant pressure transducer in the form of a mechanical resonant circuit whose characteristic frequency of mechanical vibration varies according to ambient pressure.
While the prior art intracranial pressure sensing devices and equipment like those described above, may be generally suitable for their intended purposes, they never the less leave much to be desired from the standpoints of complexity, cost, durability, range, sensitivity and reliability.